Pollen foraging behaviour of solitary Hawaiian bees revealed through molecular pollen analysis

Abstract

Obtaining quantitative information concerning pollinator behaviour has become a primary objective of pollination studies, but methodological limitations hinder progress towards this goal. Here, we use molecular genetic methods in an ecological context to demonstrate that endemic Hawaiian Hylaeus bees (Hymenoptera: Colletidae) selectively collect pollen from native plant species in Haleakala and Hawaii Volcanoes National Parks. We identified pollen DNA from the crops (internal storage organs) of 21 Hylaeus specimens stored in ethanol for up to 3 years. Genetic analyses reveal high fidelity in pollen foraging despite the availability of pollen from multiple plant species present at each study site. At high elevations in Haleakala, pollen was available from more than 12 species of flowering plants, but Hawaiian silversword (Argyroxiphium sandwicense subsp. macrocephalum) comprised 86% of all pollen samples removed from bee crops. At lower elevations in both parks, we only detected pukiawe (Leptecophylla (Styphelia) tameiameiae) pollen in Hylaeus crops despite the presence of other plant species in flower during our study. Furthermore, 100% of Hylaeus crops from which we successfully identified pollen contained native plant pollen. The molecular approaches developed in this study provide species-level information about floral visitation of Hawaiian Hylaeus that does not require specialized palynological expertise needed for high-throughput visual pollen identification. Building upon this approach, future studies can thus develop appropriate and customized criteria for assessing mixed pollen loads from a broader range of sources and from other global regions.

Pollen DNA barcoding: current applications and future prospects

“…Early studies typically relied on either direct Sanger sequencing of purified PCR amplicons (Longhi et al 2009;Wilson et al 2010), for singlespecies barcoding, or else, for multi-species samples, Sanger sequencing of amplicon clones randomly selected from PCR products (Galimberti et al 2014;Bruni et al 2015). The latter has mostly been superseded by HTS approaches for DNA metabarcoding.…”

Flower preferences and pollen transport networks for cavity‐nesting solitary bees: Implications for the design of agri‐environment schemes

“…DNA sequencing has been used successfully to identify the foraging preference of honeybees and the floral composition of their honey (Bruni et al., 2015; De Vere et al., 2017; Galimberti et al., 2014; Hawkins et al., 2015; Jain, Jesus, Marchioro, & Araújo, 2013; Valentini, Miquel, & Taberlet, 2010). Several studies have also used pollen DNA sequencing to identify solitary bee foraging preferences (Sickel et al., 2015; Wilson, Sidhu, Levan, & Holway, 2010). One challenge where DNA may provide a solution is to resolve interactions when the diversity of plants visited is high.…”

Seasonal trends in honey bee pollen foraging revealed through DNA barcoding of bee-collected pollen

“…The resulting solution was used as a DNA template for PCR. Wilson et al (2010) found that mixed pollen loads composed of multiple species (as low as 1% w/v) did not yield usable sequence data because the resulting sequences were very short and of low quality. Moreover, honey bees are floral constant and typically return to the hive with pure pollen loads (Grant 1950).…”

“…Using DNA barcodes to study plant-pollinator interactions DNA barcoding can illuminate the vital ecosystem service provided by bee pollinators (Wilson et al 2010) and help identify which plant species sustain bee populations. Researchers can identify pollen to genera or species using standard PCR and Sanger sequencing techniques, without specialist training or amassing a large library of pollen reference slides.…”